Research Of A High-Power Millimeter-wave Faraday Rotator

Nonreciprocal devices based on gyromagnetic ferrites are indispensable fundamental components in RF and microwave/millimeter-wave electronic equipment and systems. In millimeter wave system, the ferrite rotator/isolator is very important.Based on the principle of non-reciprocity, ferrite circulator and isolator have numerous applications to solve many practical problems such as isolation in radar system and between power amplifier, impedance matching and antenna duplexer.Conventional waveguide isolator applied in millimeter wave emerges some problems. With the increase of frequency, waveguide dimensions and tolerances become more critical. It has greatly increased the difficulty and precision of fabrication to meet higher standards. In addition, ohmic losses in waveguide structures increase with frequency, and the corresponding ferrite components become less efficient. Particularly,heat dissipation requirements caused by high electric fields in confined spaces is a further problem. Quasi-optical techniques utilized at millimeter wavelength offer attractive alternatives to waveguide devices where space and weight limitations are sufficiently generous to permit transmission of Gaussian beams fashioned and controlled by quasi-optical components. It can solve the problems of difficult fabrication and insufficient power capacity due to the smaller waveguide dimensions with the increase of frequency. Thus, the research of quasi-optical Faraday rotator is significant for millimeter system. Especially in the transmission line of the high power gyro-TWT, where exsist many quasi-optical transmission devices. And the Faraday rotator has a very important role in its high power capacity. The main contents of this thesis include the following aspects:(1) This thesis strictly decuced the propagation characteristics of electromagnetic waves in ferrite materials. And derived the the important propagation characteristics of microwave ferrite materials——Faraday rotation effect. In this way, the direct factors of the Faraday rotator are the thickness of the ferrite and the magnitude of the applied magnetic field;(2) This thesis designed single-layer, triple-layer and five-layer dielectric structure respectively. And the matching layer adapte the dielectric with perfect performance,which is realized by perforating many holes in the plates to reduce the effective dielectric constant to the required value. This structure have high power handing and broad withband;(3) This thesis gives the test results of the saturation magnetization of the ferrite samples and the change of the saturation magnetization with temperature. Then, to ensure the performance of Faraday rotator, steady-state themal analysis are carried out to caculate the power capacity of the two five-layer Faraday rotator;(4) This thesis designed magnet by using CST on the basis of demagnetization of ferrite. And a SMCo permanent magnet with magnetic field intensity of 1174Gauss was given;(5) This thesis design of related components for microwave measurement, such as the HE11 mode exciter and the polarization filter. In the working bandwidth, both the HE11 mode exciter and the polarization filter can ensure less power loss in the transmission.